1. Field of the Invention
The present invention relates to document scanning devices for reading an image on a document, and control methods therefor.
2. Description of the Related Art
A conventional method has been used in which document scanning devices, such as scanners, facsimile devices, and copying machines, having the function of reading an image on a document are connected to a personal computer or the like, and image data obtained by reading the image while scanning the document are transferred to the personal computer.
The types of interface between the personal computer and the document scanning devices include a bidirectional parallel interface based on the IEEE P1284, SCSI, and RS232C standards. Among these types of interfaces, the IEEE P1284 is the most common, and has various modes such as compatible mode, nybble mode, extended capabilities port (ECP) mode, byte mode, and enhanced parallel port (EPP) mode, whose transfer speeds differ greatly. The transfer speed is determined by the transfer mode and typically operates at dozens to hundreds of Kb/s, although it depends on the use of the personal computer. It is said that the universal serial bus (USB), whose transfer speed is at least 1 Mb/s, will be widely used instead of the IEEE P1284 in future.
In addition, according to the IEEE 1394 interface, data can be transferred at 100 Mbytes/s or greater.
In adaptation for various types of interface and various reading modes, the realization of the desired functions in accordance with the transfer speed and the matching of system performance with the transfer speed are important considerations. Accordingly, a system capable of flexibly adapting to various transfer modes or various types of transfer interfaces, regardless of transfer speed, is in demand.
In the case where the operation of reading an image as multiple data per pixel, such as 8-bit data per pixel is realized, the amount of the data to be transferred is eight times that of reading an image as binary data per pixel. Therefore, a data-transfer load on the system bus of the document scanning device limits the transfer speed of the interface, even when a high transfer speed is used.
Conversely, a low transfer speed causes transfer processing to require a large buffer memory capacity since the low transfer speed prevents the transfer processing from being matched with a speed at which image data are generated.